Extendible stent apparatus

ABSTRACT

The bifurcating double stent apparatus ( 10 ) of the present invention comprises a generally cylindrical main stent ( 12 ), a generally cylindrical branch stent ( 15 ), which are shown as fully dilated in a subject main vessel ( 8 ), and a subject branch vessel ( 7 ). The main stent ( 12 ) is deployed prior to the branch stent ( 15 ) which is then aligned with the side opening ( 16 ) of the main stent ( 12 ), and attached at that location.

BACKGROUND OF THE INVENTION

A type of endoprosthesis device, commonly referred to as a stent, may beplaced or implanted within a vein, artery or other tubular body organfor treating occlusions, stenoses, or aneurysms of a vessel byreinforcing the wall of the vessel or by expanding the vessel. Stentshave been used to treat dissections in blood vessel walls caused byballoon angioplasty of the coronary arteries as well as peripheralarteries and to improve angioplasty results by preventing elastic recoiland remodeling of the vessel wall. Two randomized multicenter trialshave recently shown a lower restenosis rate in stent treated coronaryarteries compared with balloon angioplasty alone (Serruys, P W et al.New England Journal of Medicine 331:489-495, 1994, Fischman, D L et al.New England Journal of Medicine 331:496-501, 1994). Stents have beensuccessfully implanted in the urinary tract, the bile duct, theesophagus and the tracheo-bronchial tree to reinforce those body organs,as well as implanted into the neurovascular, peripheral vascular,coronary, cardiac, and renal systems, among others. The term “stent” asused in this Application is a device which is intraluminally implantedwithin bodily vessels to reinforce collapsing, dissected, partiallyoccluded, weakened, diseased or abnormally dilated or small segments ofa vessel wall.

One of the drawbacks of conventional stents is that they are generallyproduced in a straight tubular configuration. The use of such stents totreat diseased vessels at or near a bifurcation (branch point) of avessel may create a risk of compromising the degree of patency of theprimary vessel and/or its branches, or the bifurcation point and alsolimits the ability to insert a second stent into the side branch if theresult of treatment of the primary, or main, vessel is suboptimal.Suboptimal results may occur as a result of several mechanisms, such asdisplacing diseased tissue, plaque shifting, vessel spasm, dissectionwith or without intimal flaps, thrombosis, and embolism.

The risk of branch compromise is increased generally in two anatomicalsituations. First, a side branch may be compromised when there is astenosis in the origin of the side branch. Second, when there is aneccentric lesion at the bifurcation site, asymmetric expansion can causeeither plaque shifting or dissection at the side branch origin. Thereare reports of attempts to solve this problem by inserting a ballooninto the side branch through the struts of a stent deployed in the mainbranch spanning the bifurcation point; however, this technique carriesthe risk of balloon entrapment and other major complications (Nakamura,S. et al. Catheterization and Cardiovascular Diagnosis 34:353-361(1995)). Moreover, adequate dilation of the side branch is limited byelastic recoil of the origin of the side branch. In addition, insertionof a traditional stent into a main vessel spanning a the bifurcationpoint may pose a limitation to blood flow and access to the side branchvessel. The term “stent jail” is often used to describe this concept. Inthis regard, the tubular slotted hinged design of the Palmaz-Schatzintracoronary stent, in particular, is felt to be unfavorable forlesions with a large side branch and is generally believed to pose ahigher risk of side branch vessel entrapment where the stent prevents orlimits access to the side branch. Id.

One common procedure for intraluminally implanting a stent is to firstopen the relevant region of the vessel with a balloon catheter and thenplace the stent in a position that bridges the treated portion of thevessel in order to prevent elastic recoil and restenosis of thatsegment. The angioplasty of the bifurcation lesion has traditionallybeen performed using the “kissing” balloon technique where twoguidewires and two balloons are inserted, one into the main branch andthe other into the side branch. Stent placement in this situationrequires the removal of the guidewire from the side branch andreinsertion through the stent struts, followed by the insertion of aballoon through the struts of the stent along the guidewire. The firstremoval of the guidewire poses the risk of occlusion of the side branchduring the deployment of the stent in the main branch.

In general, when treating a bifurcation lesion using commerciallyavailable stents, it is important to cover the origin of the branchbecause if left uncovered, this area is prone to restenosis. In order tocover the branch origin, conventional stents inserted into the branchmust protrude into the lumen of the main artery or vessel from thebranch (which may cause thrombosis, again compromising blood flow).Another frequent complication experienced when stenting bifurcatedvessels is the narrowing or occlusion of the origin of a side branchspanned by a stent placed in the main branch. Additionally, placement ofa stent into a main vessel where the stent partially or completelyextends across the opening of a branch makes future access into suchbranch vessels difficult if not impossible. As a result, conventionalstents are often placed into the branch close to the origin, butgenerally not covering the origin of the bifurcation.

Lastly, conventional stents are difficult to visualize during and afterdeployment, and in general are not readily imaged by using low-cost andeasy methods such as x-ray or ultrasound imaging. While some prior artballoon catheters (and not stents) are “marked” at the proximal anddistal ends of the balloon with imageable patches, few stents arecurrently available which are marked with or which are at least partlyconstructed of, a material which is imageable by currently known imagingprocedures commonly used when inserting the stents into a vessel, suchas ultrasound or x-ray imaging. The invention described in thisApplication would not work with endoscopy as currently used as animaging method due to size limitations, but future advances in limitingthe size of endoscopic imaging devices may in the future make endoscopicimaging compatible with the stents of the invention.

Accordingly, there is a need for improved stent apparatuses, mostparticularly for applications within the cardiac, coronary, renal,peripheral vascular, gastrointestinal, pulmonary, urinary andneurovascular systems and the brain which 1) completely covers thebifurcation point of bifurcation vessels; 2) may be used to treatlesions in one branch of a bifurcation while preserving access to theother branch for future treatment; 3) allows for differential sizing ofthe stents in a bifurcated stent apparatus even after the main stent isimplanted; 4) may be delivered intraluminally by catheter; 5) may beused to treat bifurcation lesions in a bifurcated vessel where thebranch vessel extends from the side of the main vessel; and 6) is markedwith, or at least partly constructed of, material which is imageable bycommonly used intraluminal catheterization visualization techniquesincluding but not limited to ultrasound or x-ray.

SUMMARY OF THE INVENTION

The present invention concerns novel stent apparatuses for methods, andkits use in treating lesions at or near the bifurcation point inbifurcated vessels. More particularly, the invention concerns a stentapparatus with a main tubular stent body having at least one sideopening which may further comprise an extendable or second stentinserted through the side opening and at least partly in registry withthe wall of the side opening.

As used herein, the term “vessel” means any body lumen or tubular tissuewithin the cardiac, coronary, renal, peripheral vascular,gastrointestinal, pulmonary, urinary and neurovascular systems and thebrain. Devices constructed in accordance with the invention include,singularly or in combination, a main expandable tubular stent bodyhaving at least one side opening (usually substantially circular)located between its proximal and distal end openings, which side openingmay further comprise a radially expandable portion extending laterallyoutward from the edges of the side opening; and an expandable branchsecond stent comprising proximal and distal end openings and which mayfurther comprise a contacting portion at its proximal end, and which maybe constructed to form an angularly variable branched stent apparatuswhen inserted through a side opening of the main stent. The radiallyexpandable portion preferably comprises a plurality of laterallydeployable elements, such as loops, tabs, beams, or the like, attachedor coupled to a peripheral edge of the side opening. Usually, theelements will project inwardly from the periphery into the side hole sothat they may be deployed radially outwardly from the periphery to openin a petal-like fashion. The elements may be formed integrally as partof the tubular body structure, e.g., being formed from the bent wire orband or from the cut tubular structure which defines the stentstructure. Alternatively, they could be formed separately andsubsequently attached by crimping, welding, folding, interferencefitting, etc. Optionally, the expandable portion may be covered with afabric or the entire stent structure membrane to help form thetransition between the main body lumen and the lumen of the secondstent. The stents of the invention are marked with, or at leastpartially constructed of, a material which is imageable duringintraluminal catheterization techniques, most preferably but not limitedto ultrasound and x-ray, preferably being radiopaque.

In a preferred aspect of the stent design, the side hole will be definedby a continuous band or pattern of material which defines the peripheryof the side hole. The band may have a circular, oval, or other regulargeometry in which case the width and area of the side hole will remaingenerally constant as the stent is expanded. Alternatively, thecontinuous band may comprise discontinuities over its length so that thearea and/or width of the side hole may expand together with the stentstructure. Preferably, the continuous band will include inwardlyprojecting loops, fingers, or other protrusions which will define thelaterally deployable elements which project inwardly from the peripheraledge of the side opening. The inwardly projecting loops or otherelements may be overlapping or non-overlapping. The use of overlappinglooped structures maximizes the length of the inwardly projectingelements after they are unfolded and opened inwardly into the sidebranch, as described in more detail below.

In another aspect of the present invention, a stent for placement in abifurcated body lumen comprises a main tubular body having a first end,a second end, and a side opening therebetween. A first portion of themain tubular body between the first end and the side hole opens inresponse to a first radially outward pressure, typically provided by anexpansion balloon. A second portion of the main tubular body between theside hole and the second end opens in response to a second pressure,again typically applied by an expansion balloon. By constructing themain tubular body so that the first opening pressure is less than thesecond opening pressure, the stent can have differential openingcharacteristics. That is, by introducing a balloon expansion catheterinto the stent and applying a constant pressure over the entire lengthof the balloon, the first portion of the stent will yield and openbefore the second portion of the stent. The particular embodimentsdescribed below, the first yield pressure will typically be in the rangefrom 1 atmospheres to 10 atmospheres while the second yield pressurewill typically be in the range from 2 atmospheres to 18 atmospheres.Such stent structures may be placed by initially opening and deployingthe first portion, typically the proximal portion on the same side ofthe bifurcation as the deployment catheter, and thereafter positioningthe side hole to align more precisely with the bifurcated secondaryblood vessel. After the proper positioning has been achieved, the secondstent portion can then be opened, conveniently using the same expansionballoon which has been inflated to a higher inflation pressure. Suchstents will typically include the laterally deployable elements disposedaround the side opening, as described above, and will optionally be usedin combination with secondary stents, as described above.

The stent structures as described previously may combine conventionalstent elements, such as serpentine rings, diamond or box structures,axial expansion members, and the like. In addition, in order to providethe differential expansion characteristics, the main tubular bodies ofthe stents may include axial spine structures which differ from theremaining portions of the tubular body of the stent. For example, thefirst portion of the stent may have an axial spine which readily expandscircumferentially. By then providing a spine section on the secondportion of the stent which is more resistant to circumferentialexpansion, the desired differential expansion will be achieved.Alternatively, the differential expansion can be achieved by employingstent patterns which are uniformly easier or more difficult to radiallyexpand over their entire peripheral length. Specific examples of bothstructures will be described below.

The stent apparatuses of the invention offers significant and noveladvantages over prior art stents in that the stents of the invention 1)can completely cover the bifurcation point of a branched vessel; 2) canaccommodate main and branch stents of differing sizes, thus providing abetter fit where the main and branch vessels are occluded to differentdegrees; 3) can fit branched vessels where the branch extends laterallyfrom the side of the main vessel; 4) may be used to treat lesions in onebranch of a bifuircation while preserving complete access to the otherbranch for future treatment; 5) may be delivered intraluminally bycatheter; and 6) are marked with, or at least partly constructed of,material which is imageable by commonly used intraluminalcatheterization visualization techniques including but not limited toultrasound or x-ray, but not endoscopy.

Thus, it is an object of the present invention to provide both adouble-stent apparatus and a single-stent apparatus, each of which maybe used to cover the origin of a bifurcation in a branched vessel.

Another object of the invention is to provide a single-stent apparatuswhich may be used to treat only one branch of a bifurcation lesion whileleaving access to the second branch unobstructed.

Additionally, it is an object of the invention to provide a stentapparatus which is itself imageable by methods commonly used duringcatheterization such as x-ray or ultrasound.

Yet another object of the invention is to provide a bifurcatingdouble-stent device wherein the main stent and the branch stent orstents may be of different sizes.

Lastly, it is an important object of the invention to provide a stentapparatus which may be used to treat bifurcated vessels where the vesselbifurcation extends laterally from the side of the main vessel.

These objects and other object advantages and features of the inventionwill become better understood from the detailed description of theinvention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of the double-stent apparatus of thepresent invention in which both the main stent and the branch stent arefully dilated.

FIG. 2 is a schematic depiction of the main stent of the apparatus ofthe invention as deployed, with the side opening in registry with avessel bifurcation point.

FIG. 3 is a schematic depiction of the branch stent of the apparatus asdeployed, with the contacting portion fully expanded to contact theorigin of the bifurcated vessel.

FIG. 4 is a schematic depiction of the main stent of the apparatusdeployed within a subject vessel, after inflation of a balloon to expandthe main stent to fit the walls of the subject vessel.

FIG. 5 is a schematic depiction of the double-stent bifurcating stentapparatus, where the main stent is deployed and showing the placement ofthe branch stent apparatus prior to full deployment of the branch stent.

FIG. 6 a depicts initial placement of the main stent of the bifurcatingstent apparatus into the vessel, along with the insertion of a guidewireand stabilizing catheter for placement of the branch stent into thebranch vessel of the subject.

Fib. 6 b is a schematic depiction showing the main stent of theinvention expanded by balloon expansion.

FIG. 6 c is a schematic depiction of the deployment of the branch stentover the side branch guidewire, through one of the side openings in themain stent and into the branch vessel of the subject.

FIG. 6 d is a schematic depiction of the removal of the protectivesheath of the branch stent allowing for full expansion of the contactingportion prior to final placement and deployment.

FIG. 6 e is a schematic depiction of the compressed branch stentpositioned into the branch by the catheter with the contacting portionat least partly contacting the side opening in the main stent, but priorto full expansion of the branch stent.

FIG. 6 f is a schematic depiction of the fully expanded main stent andthe fully positioned and expanded branch stent, where the branch stentis being dilated by inflation of a balloon.

FIG. 6 g is a schematic depiction of the fully expanded bifurcatingdouble stent of the invention, positioned into the bifurcation point ina subject vessel.

FIG. 7 is a schematic depiction of the main stent with optionalexpandable portion, prior to balloon expansion of the expandableportion.

FIG. 8 is a schematic depiction of balloon expansion of the optionalexpandable portion of the main stent to cover a vessel bifurcationpoint.

FIG. 9 is a schematic depiction of the main stent with the optionalexpandable portion fully expanded to extend laterally from the sideopening of the main stent.

FIG. 10 illustrates a first stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

FIG. 11 illustrates a second stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

FIG. 12 illustrates a third stent pattern having a side hole anddifferential expansion characteristics in a “rolled out” view.

FIGS. 13A-13H illustrate the deployment of any one of the stents ofFIGS. 10-12 in a bifurcated blood vessel or a secondary stent is placedthrough the side hole of the main stent.

The rectilinear matrices shown in the drawings are intended to show theshapes of the surfaces only, and do not illustrate the actual surfacepatterns or appearances of the stent apparatuses of the invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The bifurcating double-stent apparatus 10 of the present inventioncomprises a generally cylindrical main stent 12 and a generallycylindrical branch stent 15, which are shown as fully dilated in asubject main vessel 8 and a subject branch vessel 7, as illustrated inFIG. 1.

The main stent 12 contains at least one generally circular side opening16 located between the proximal end 26 and the distal end 28 of the mainstent 12 (FIG. 2), which opening is positioned over and in registry withthe opening 48 of a branch vessel in a vessel bifurcation 50, as shownin FIG. 2. The stent 12 and the side opening are imaged during imagingprocedures either by constructing the stent of imageable materials or byplacing markers 56 at appropriate locations, such as around theperimeter of the side opening 16 in the main stent 12, and at theproximal end 26 and distal end 28 of the main stent, as illustrated inFIG. 4.

As shown in the embodiment of the invention illustrated in FIG. 4, aguidewire 20 is inserted into the vessel 8 prior to insertion of themain stent 12, and is used to guide the main stent 12 into positionwithin the vessel 8. Prior to insertion and expansion, the main stent 12Is disposed around the distal end of a catheter 48 which may include aninflatable balloon 24. The main stent/catheter apparatus is thenthreaded onto the main guidewire 20 and into the vessel 8. The mainstent 12 is radially expanded by inflation of the balloon 24 until itexpands the walls of the vessel 8, and is thus affixed into place.

In a second embodiment of the invention, the branch stent apparatus 15of the present invention comprises a generally cylindrical stentcomprising a proximal end 30 and a distal end 32, as shown in FIG. 3.The proximal end 30 comprises a contacting portion illustrated here asextended loops 18, which contacting portion, when expanded, ispositioned within the lumen 58 of the main vessel 8 (FIG. 3) and atleast partially contacting the perimeter of the side opening 16 of themain stent 12. FIG. 4 illustrates the positioning of the main stent 12(without optional contacting portion) in the main vessel 8 as fullyexpanded by inflation of the balloon 24.

As shown in the embodiments illustrated in FIGS. 4, 5 and 7, the ends ofthe main stent 12 and the expandable branch stent 15 and the contactingportion 18 are visible during insertion by placing imageable markers 56around the ends of the main 12 and branch 15 stents and the contactingportion 18 and at the proximal end 30 and distal end 32 of the branchstent. Alternatively, the stent may be at least partially constructed ofmaterial which is imageable by methods including but not limited toultrasound or x-ray imaging (but not endoscopic imaging).

As shown in yet another embodiment, the stents of the invention arecombined to form a bifurcating double stent as illustrated in FIGS. 5and 6 a-g. After insertion of the main stent as described above butprior to expansion of the main stent (FIG. 6 a), the branch stent 15 isinserted through a side opening 16 of the main stent 12, a guidewire 36and a stabilizing catheter 44 are inserted through the side opening 16in the main stent 12, and into a branch vessel 7 (FIG. 6 a). Thestabilizing catheter 44 is used to place the side opening 16 in the mainstent 12 over the bifurcation point 50 in the bifurcated vessels 7 and 8(FIG. 6 a). In the embodiment depicted here, the main stent is thendeployed into position by inflation of the balloon 24 (FIG. 6 b). Duringinsertion and prior to dilation of the branch stent, the branch stent 15is disposed around the distal end of a branch catheter 54 which mayoptionally include an inflatable balloon 25, and the contacting portion18 of the branch stent 15 is held in a collapsed position by aprotective sheath 34, as shown in FIG. 6 c.

In the bifurcating double-stent apparatus 10 of the invention, once themain stent 12 is dilated and the stabilizing catheter 44 (as shown inFIG. 6 b) is removed, the branch stent 15 is inserted over the branchguidewire 36 and through the opening 16 of the main stent 12substantially as shown in FIG. 6 c, and affixed in place by withdrawalof the protective sheath 34 (FIG. 6 d) and insertion of the branch stent15 until at it least partially contacts the perimeter of the opening 16of the main stent 12 by the expansion of the contacting portions 18which are positioned at the proximal end 30 of the expandable stent, asshown in FIG. 6 e. The branch stent 15, once positioned in the branchvessel 7, may be then fully expanded by the balloon 25, as shown in FIG.6 f. The angle at which the optionally expandable branch stent 15 isaffixed depends upon the vessel structure into which the bifurcatingstent apparatus 10 is inserted. All catheters and guidewires are thenwithdrawn from the subject vessels, leaving the main stent 12 throughwhich the branch stent 15 is inserted into the branch vessel 7, forminga bifurcated stent 10 (FIG. 6 g).

As illustrated in FIGS. 6 a-6 g, the main stent 12 is deployed prior tothe branch stent 15. This is the presently preferred order ofdeployment. It will be possible, however, in some circumstances todeliver the branch stent 15 prior to the main stent 12. In such cases,the branch stent 15 will be deployed with the contacting portions 18opened directly against the inner wall of the main blood vessel. Themain stent 12 will then be positioned over the contacting portions 18 ofthe branch stent 15 and firmly expanded thereagainst. A sheath orexpansion balloon can be used to properly align the side opening 16 ofthe main stent 12 with the opening within the contacting portion 18 ofthe branch stent 15.

In the embodiment shown in FIGS. 7-9, the main stent 40 with expandableportion 38 is positioned within the vessel 8 by the guidewires 20 (FIG.7), and affixed in place by radial expansion of the main stent 40, mostparticularly by inflation of the balloon 25 (FIG. 8). The main stent ispositioned so that the opening 16 is directly over the bifurcation point50 in the subject vessels 7 and 8 (FIG. 7 and 8). In order to aid suchpositioning, a side branch guidewire 36 and a stabilizing catheter 44(as depicted in FIG. 7) are also inserted through the opening 16 of themain stent 40 and through the expandable portion 38 and into the branchvessel 7 (FIG. 8).

The optional expandable portion 38 of the main stent 40 is then expandedradially and in an at least partially perpendicular manner to the sidesof the main stent side opening 16 (FIG. 8). In the embodimentillustrated in FIGS. 7 and 8, a balloon 25 is deployed along the sidebranch guidewire 36 through the expandable portion 38, and inflateduntil the expandable portion is fully expanded into the branch vessel 7to cover the bifurcation point 50 of the branched vessel, as illustratedin FIG. 8. In order to extend the expandable portion 38 into the branchvessel 7, a balloon 25 disposed around a branch catheter 54 which isthreaded along the side branch guidewire 36, through the main stent 40,through the opening 16 and expandable portion 38, and into the subjectbranch vessel 7 as shown in FIG. 8. The expandable portion 38 is thenextended into the branch vessel 7 by inflation of the balloon 25, whichpushes the expandable portion 38 outward radially and lateral to theside opening, into the branch vessel 7 (FIG. 8). Once all catheters andballoons are withdrawn, the expandable portion 38 is arrayed in lateralorientation to the sides of the opening 16 in the main stent 40, andsurrounding the opening 16 into the vessel branch (FIG. 9). Theguidewires 20 and 36 are then withdrawn from the main and branchvessels.

The expandable portion 38 is illustrated as a plurality of elementswhich are attached to the peripheral edge of the side opening 16. Theelements project radially inwardly into the side opening and thus liewithin the cylindrical envelope of the tubular main stent 40 prior todeployment, as shown in FIG. 7. The elements are opened by outwardlateral defection, typically using a balloon catheter, as illustrated inFIG. 8. The deflected elements both traverse the transition between thestent and the lumen of the branch vessel and also serve as an anchor forsubsequent placement of the second stent.

In the double stent apparatus of FIG. 5 and in the main stent withexpandable portion illustrated in FIGS. 7 and 9, the main stent as wellas the expandable portions may be constructed at least partially ofand/or coated or plated with an imageable material or marked withimageable markers 56 at suitable locations, including around theperimeter of the side openings of the main stent and at the ends of theexpandable portions. In the differentially expandable stent structuresof FIGS. 10-12 (described below), a distal portion may be radiopaquewith the remainder being radiolucent. Suitable imageable materials areradiopaque, such as gold, tungsten, and the like.

When reinforcing a bifurcated vessel where both branches of the vesselrequire reinforcing, either 1) the single main stent with the expandableportion is used whereby the expandable portion extends into the vesselbranch at least partly covering the origin of the bifurcation, which maybe used alone or in combination with any conventional stent; or 2) themain stent without the expandable portion and at least one branch stentwith contacting portion are used, the branch stent placed to extendthrough at least one side opening of the main stent into at least onebranch vessel, wherein the branch stent is at least partially inregistry and contacting the edge of the side opening through which itextends. The branch stent extends laterally at varying angles to theside opening of the main stent. When treating a bifurcated vessel wherethe area to he treated spans the bifurcation and unobstructed access tothe unstented vessel is required, the main stent may be used either withor without the expandable portion, wherein at least one side opening isplaced over the bifurcation point.

The stent apparatus of the invention may be construed from anynon-immunoreactive material, including but not limited to any of thematerials disclosed in the prior art stents which are incorporatedherein by reference. It is intended that the stent apparatuses of theinvention may further be at least partially constructed of, or marked atcertain points with, a material which may be imaged, most particularlybut not limited to by x-ray and ultrasound.

The stents of the invention may be deployed according to known methodsutilizing guidewires and catheters, which are then withdrawn from thesubject following deployment of the stents. The subject stents may beself-expanding to conform to the shape of the vessel in which they aredeployed, or they may be expanded utilizing balloon catheters, or by anyother method currently known or developed in the future which iseffective for expanding the stents of the invention. It is contemplatedthat prior to deployment the stents will be in a collapsed state, andwill require either mechanical expansion (such as, for example, byballoon expansion) upon deployment or, for self-expanding stents, willrequire that the stent be confined to the catheter until deployment by,for instance, a retractable sheath, in which the sheath is removedduring deployment and the stent self-dilated. The stents of theinvention and the optional expandable portion of the main stent of theinvention expand radially from their longitudinal axis, lateral to theside opening of the main stent. Other methods of dilation of the stentsof the invention may exist, or may become available in the future, andsuch methods are contemplated as being within the scope of thisinvention.

Referring now to FIGS. 10-12, the present invention further providesstent structures having differential radial expansion characteristics.In particular, tubular stent structures having side holes, generally asdescribed above, are configured so that a portion of the stent on oneside of the side hole will expand at a different yield or thresholdforce than a portion of the stent on the other side of the side hole.Such different yield forces or pressures may be achieved in a variety ofways. For example, referring to FIG. 10, a stent 100 is illustrated in a“rolled out” view, i.e., the tubular stent is broken along an axial lineand then rolled out in the resulting pattern shown in the Figure. Thepattern shown in FIG. 10 is prior to expansion. The stent 100 includes aside hole 102 defined by a continuous band 104 having a plurality ofloops 106 projecting into the open interior of the side hole. The loops106 are an integral part of the band 104 and will, prior to expansion oropening, lie within the cylindrical envelope of the tubular body of thestent. The first portion 110 of the stent lies on one side of the sidehole 102 and is defined by a plurality of serpentine rings 112. Theserpentine rings are joined by axial expansion spring structures 114 sothat the stent may be bent as it is introduced and/or deployed. A secondportion 120 of the stent 100 is formed on the other side of side hole102. The second portion is also defined by the plurality of serpentinerings 122 which are generally similar in structure to the rings 112 ofthe first portion 110. Each of the portions 110 and 120, however,include an axial spine 130 and 132. The axial spine 130 of the firstportion 110 comprises simple W-shaped structures including outermoststruts 134 which open at a relatively low expansion force on theadjoining hinge regions. In contrast, the axial spine 132 of the secondportion 120 comprises box elements 138 which require a greater expansionforce to open. Thus, in deployment, the first portion 110 will yieldfirst to allow partial opening before the second portion 120 begins toopen.

A second stent structure 200 having differential expansioncharacteristics is illustrated in FIG. 11. A side hole 202 is formedfrom a continuous band of material, generally as described for FIG. 10.A first portion 204 and a second portion 206 of the stent each comprisea plurality of serpentine ring structures 208 and 210, respectively.While the specific geometries differ, the structures of stents 100 and200 are generally the same, except for axial spine portions 220 and 230in the first portion 204 and a second portion 206, respectively. Thefirst spine portion 220 comprises a simple U-shaped loop having a pairof struts joined by a simple C-shaped hinge region. The spine 220 willthus open at relatively low expansion forces. In contrast, the axialspine 230 of the second portion 206 comprises a serpentine element whichallows for axial expansion but does not permit radial expansion at all.Thus, the first portion 204 will begin opening at much lower expansionforces or pressures than will the second portion 206.

A third concept for providing differential expansion is illustrated inFIG. 12. Stent 300 comprises a side hole 302 (which is shown in halvesin the illustration), a first portion 304, and a second portion 306. Thefirst portion 304 and second portion 306 each comprise serpentine rings308 and 310, respectively. Differential expansion, however, is notachieved by providing a particular axial spine region, but rather byhaving different characteristics in the serpentine rings 308 and 310.The serpentine rings 308 have partially axially aligned struts joined bysimple hinge regions. The length of the struts is relatively long(compared to those in the second portion 306 as described below) so thatthe rings will open at a lower expansion pressure or force. Theserpentine rings 310 of the second portion 306 have relatively shortaxial struts defined by hinge regions each having two bands. Suchstructures require a greater expansion force than do the serpentinerings 308 of the first portion.

It will be appreciated that numerous other specific designs may beprovided for differential expansion. What is important to the presentinvention, however, is that at least a portion of the stent on one sideof the side hole, usually the entire length of the stent on that side ofthe side hole, will be able to open prior to opening of the stent on theother side of the side hole. Preferably, the first portion of the stentwill open at a balloon expansion pressure in a range from 1 atmospheresto 10 atmospheres, while the second portion of the stent will open inresponse to a balloon expansion pressure in the range from 2 atmospheresto 18 atmospheres.

Referring now to FIGS. 13A-13H, deployment of stent 100 will bedescribed. While reference is made to stent 100, it will be appreciatedthat the same method could be used as well with either of stents 200 or300. Initially, a pair of guidewires GW1 and GW2 will be deployed in thelumen, typically a bifurcated blood vessel, so that guidewire GW1extends through the main lumen of the main vessel past the ostium O ofthe branch vessel BRV. The second guidewire GW2 will be advanced throughthe lumen of the main vessel and into the lumen of the branch vesselBRV, as illustrated in FIG. 13A. The stent 100 will then be introducedover the guidewires on a delivery catheter 400 having an expansionballoon 402, where the stent is crimped over the expansion balloon. Asheath 404 is disposed in the second portion 120 of the stent with itsdistal tip (not shown) terminating immediately before the side opening102. The assembly of the stent 100, delivery catheter 400, and sheath404 will be delivered with the first guidewire GW1 passing through aguidewire lumen of catheter 400 and the second guidewire GW2 passingthrough the sheath 404, as illustrated in FIG. 13B. Initial alignment ofthe side hole 102 of stent 100 is achieved by advancing the stent sothat the side hole lies close to the ostium O.

After an initial rough alignment is achieved, the balloon 402 isinflated to an initial inflation pressure which opens the first portion110 but which leaves the second portion 120 in its substantiallyunexpanded configuration, as shown in FIG. 13C. Such partial openingallows the sheath 404 to be advanced over guidewire GW2 to better alignthe side hole with the branch vessel BRV, as shown in FIG. 13D. Thesheath provides much greater stiffness than the guidewire, permittingmanipulation of the partially deployed stent 100 to achieve betteralignment.

Referring now to FIG. 13E, after alignment is achieved, the balloon 402will be inflated to a greater inflation pressure to open the secondportion 120 of the stent 100 as well. A balloon catheter can then beadvanced over the second guidewire GW2 so that balloon 502 can beexpanded within the side opening 102 to open the loops 106, asillustrated in FIG. 13F. In many cases, this will be sufficientdeployment for the stent where the loops provide the necessary anchoringand transition at the ostium O.

Optionally, a secondary stent 600 may be introduced as illustrated inFIGS. 13G and 13H. The stent 600 is introduced over a balloon 702 onballoon catheter 700. The final deployment configuration is illustratedin FIG. 13H.

It is intended that the invention include all modifications andalterations from the disclosed embodiments that fall within the scope ofthe claims of the invention.

1. A stent for placement in a bifurcated body lumen having a main branchand a side branch, said stent comprising: a main tubular stent bodyhaving a first end, a second end, a lumen therethrough, and a sideopening having a plurality of laterally deployable elements therein. 2.A stent as in claim 1, wherein the elements are formed as an integralpart of the stent body.
 3. A stent as in claim 2, wherein, prior todeployment, the laterally deployable elements are aligned in a tubularenvelope defined by the tubular stent body.
 4. A stent as in claim 1,wherein the main tubular stent body is deformable so that it may beexpanded by a balloon catheter.
 5. A stent as in claim 1, wherein themain tubular stent body is deformable so that it may be expanded by aballoon catheter.
 6. A stent as in claim 1, wherein at least a portionof the main stent body is radiopaque.
 7. A stent as in claim 6, whereinat least a portion of the main stent body is radiopaque.
 8. A stent asin claim 1, having a radially compressed configuration, wherein thelength is less than 4 cm and the diameter is less than 2 cm.
 9. A stentas in claim 1, wherein the side hole comprises a continuous band.
 10. Astent as in claim 9, wherein the laterally deployable elements areinwardly projecting loops of the continuous band.
 11. A stent forplacement in a bifurcated body lumen, said stent comprising: a maintubular body having a first end, a second end, and a side openingbetween said ends, wherein a first portion of the main tubular bodybetween the first end and the side hole opens in response to a firstradially outward pressure and a second portion of the main tubular bodybetween the side hole and the second end opens in response to a secondpressure, wherein the first pressure is less than the second pressure.12. A stent as in claim 11, wherein the first pressure is in the rangefrom 1 atmospheres to 10 atmospheres and the second pressure is in therange from 2 atmospheres to 18 atmospheres.
 13. A stent as in claim 11,wherein the first portion has a first axial spine and the second portionhas a second axial spine, wherein the first axial spine openscircumferentially to a first force and the second axial spine openscircumferentially in response to a second force, wherein the first forceis less than the second force.
 14. A stent as in claim 11, wherein thefirst portion comprises serpentine rings with a first strut length andthe second portion comprises serpentine rings with a second strutlength, wherein the first strut length is greater than the second strutlength.
 15. (Canceled)
 16. A method for attaching a second stent to afirst stent, said method comprising: expanding a main tubular stentbody; and laterally deflecting a plurality of elements disposed about aside opening on the main tubular stent body.
 17. A method as in claim16, further comprising placing a second stent into the side hole so thatsaid second stent engages the laterally deflected element. 18.(Canceled)
 19. (Canceled)
 20. (Canceled)
 21. (Canceled)